The present invention relates generally to an engine retarding device for an internal combustion engine and more particularly to a method and system for compression brake actuation.
Compression brakes or engine retarders are used to assist and supplement wheel brakes in slowing heavy vehicles, such as tractor-trailers. Compression brakes are desirable because they help alleviate wheel brake overheating. As vehicle design and technology have advanced, hauling capacity of tractor-trailers has increased, while at the same time rolling resistance and wind resistance have decreased. Thus, there is a need for advanced engine braking systems in today""s heavy vehicles.
Known engine compression brakes convert an internal combustion engine from a power generating unit into a power consuming air compressor. Typically, an exhaust valve located in a combustion cylinder opens when a piston in the cylinder nears a top dead center (TDC) position on a compression stroke.
In an effort to maximize braking power, some systems open the exhaust valve of each cylinder during a first opening event and a second opening event. In this manner, pressure released from a first cylinder into the exhaust manifold is used to boost the pressure of a second cylinder. Thereafter, the pressure in the second cylinder is further increased during the upstroke of the associated piston so that retarding forces are similarly increased. This mode of operation is termed xe2x80x9cback-fillingxe2x80x9d and is disclosed in U.S. Pat. No. 5,724,939 issued to Faletti et al on Mar. 10, 1998.
Systems employing xe2x80x9cback-fillingxe2x80x9d may require opening the exhaust valves twice during the compression or exhaust cycles. During a first opening event, the piston is at or near bottom dead center (BDC). During a second opening event, the piston is at or near TDC and pressures in the cylinder typically are higher than pressures in the cylinder during the first opening event. Forces required to move the exhaust valve during the second opening event are greater than those in the first opening event. Systems are typically designed to meet the higher opening forces required in the second opening event. Operating the exhaust valve with these higher opening forces may cause an exhaust valve actuating device to impact the exhaust valve or loose contact with exhaust valve during when acting against the lower opening forces present in the first opening event. Loosing contact between the exhaust valve and valve actuating device or xe2x80x9covershootxe2x80x9d reduces controllability of the valve opening events. Further, impact between the exhaust valve and valve actuating device may cause premature wear of both the valve actuating device and the valve.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention a compression brake actuation device for an internal combustion engine has a brake actuator cylinder with a brake actuator piston. The brake actuator piston has a first actuating surface and a second actuating surface. The brake actuator cylinder and the first actuating surface define a first actuator volume. The brake actuator cylinder and the second actuating surface define a second actuator volume. A first fluid conduit is in fluid communication with the first actuator volume. The second fluid conduit is in fluid communication with the second actuator volume.
In another aspect of the present invention a method of operating a compression brake actuation system discloses pressurizing a first actuator volume. Fluid is controllably drained from a second volume. A brake actuator moves the brake actuator piston in response to the pressurizing and draining steps.